The broad objective of this study is to develop new approaches to the treatment of human allergic diseases through a more precise understanding of the structure and function of mast cells and basophil leukocytes. The basis for the allergic reaction is the sensitization of these cells by IgE antibodies and the release of biologically active mediators upon reaction with specific allergen. A transplantable mouse mast cell tumor retains the ability to bind mouse IgE antibodies and to synthesize histamine. This tumor provides a source of histidine decarboxylase (HDase), the enzyme which synthesizes histamine. HDase will be purified and an antibody prepared against it to study its localization and metabolism. Genetic variations in HDase of rat mast cells will be studied in detail. We have prepared specific antibody against rat mast cells; its effects on rat mast cells in vitro and in vivo will be studied, with the aim of understanding the kinetics of mast cells in various tissues. Finally, we will continue to collaborate with Dr. Robin Hastie in a study of the ultrastructural changes accompanying antigen induced histamine release from human basophil leukocytes.